Prior clock systems include time indicating devices to indicate sunrise and sunset times dependent upon global geographical locations. It is frequently desirable to be able to know the time of sunrise and sunset in a specified geographical location now that world wide travel and relations have expanded. As an example, a travel agency may use such a clock system due to the fact that travelers frequently want to be advised on light conditions at their destination to plan arrival or departure times to and from a different geographical location.
There are clock systems known in the prior art where daylight conditions can be indicated dependent on geographical location. The prior art systems have been based on mechanically rotated devices, such as a globe, or graphing devices to determine the daylight conditions dependent upon date and geographical location.
One type of a global device includes a rotating circular globe, a stationary cap, and a lighting means within the globe to illuminate half of the globe at a time representative of light conditions. A stationary arrow extends from the cap, wherein it is set in a notch indicating a time zone. The arrow extends to the equator of the globe which indicates time. The globe will rotate causing a result in change of time indicated by the arrow and change in light conditions of a particular location. The U.S. Pat. No. 3,516,243 granted June 23, 1970 in the name of Allyn B. Hazard, discloses a global system which uses a rotating globe with a stationary light means and time arrow. An inadequacy of this type of system is that the change in light conditions between light and dark is dependent upon month only, and indicates only an abrupt change from light to dark, and vise versa.
Another graphing device uses a clock face with disks in the center which can be rotated. A map of the United States is used in conjunction with the clock to determine longitude and latitude data which is transformed into minutes to apply when rotating the center disk. An arc is used to represent the month, wherein the exact date of location is to be estimated within the arc. By drawing a line through from the center point through the arc, sunrise and sunset times are indicated. The U.S. Pat. No. 4,551,027 granted Nov. 5, 1985 in the name of George T. Spruck discloses a graphing system wherein a rotating disc clock is used in conjunction with a geographical map to determine sunrise and sunset times in a specified geographical locations. An inadequacy of this system is the necessity of two references which when used together will determine only sunrise and sunset times.